Japanese Laid-open Patent Publication No. 2002-204493 discusses a technique of picking up a target sound with a microphone with the target sound emphasized. According to the technique, a directivity of the microphone is controlled to restrict a background noise. For example, by narrowing a directivity of a microphone array, a noise reduction quantity is increased. However, if a relative positional relationship between a sound source of a target sound and a microphone changes during sound pickup, the sound source may be off-aligned with the directivity of the microphone, and the target sound may be suppressed.
For example, the directivity of a microphone array may be narrowed on the microphone array mounted on a cellular phone. If a user holds a cellular phone at a tilt angle, the microphone array may face from the mouth of a user and the level of a sound picked up by the microphone array may be suppressed. If the user talks while walking, the positional relationship between the mouth and the microphone array is not stabilized, and the position of the mouth falls out of the directivity of the microphone array. The sound level is thus suppressed.
In a method of controlling the directivity of the microphone, a direction to the mouth, i.e., a sound source is estimated based on a sound signal picked up by the microphone array in order to control the directivity of the microphone array. This method provides a low detection accuracy of the sound source direction if signal to noise rate (SNR) is low. Japanese Laid-open Patent Publication No. 2008-167323 discusses a method of correcting a directivity of a microphone. In the method, a directivity correction value of the microphone is stored with a tilt angle of a cellular phone having the microphone mounted thereon mapped thereto on a database. By referencing the database, the directivity is corrected in response to the tilt angle of the cellular phone detected by a tilt sensor.